34: How to clean input selector switches S1 to S8 on button board

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18-Oct-2019 02:07 PM

Fabian

Fabian

Posts: 102

The Quad 34 service manual mentions cleaning the input switches, stating that these clicks might be caused by dirty switches. The service manual explicitly recommends the use of WD40 for this task, but gives no hint on how to apply it.

Searching the forum, I already found out that EJP is NOT exactly a fan of WD40 for cleaning switches and I am fine with using isopropyl alcohol instead.

I did find references to cleaning the switches on a 33, but not on a 34 or 44, so how would I do it? Do I need to pull the buttons from the switches? If so, I will have to remove the turning knobs and the front plate, right?

Has anybody done this before? I do have some clicking noise when pushing the buttons on my already revised 34.
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18-Oct-2019 07:08 PM

Stefaan

Stefaan

Posts: 618


Kontakt 60 is made for this:

http://www.dadaelectronics.eu/shop/chemicals/kontakt-chemie-61-contact-spray-200ml

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18-Oct-2019 09:09 PM

Fabian

Fabian

Posts: 102

The last can I had ordered from the Webshop started to leak within days. :)

Still, the main question is how to apply it?

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19-Oct-2019 08:51 AM

EJP

EJP

Posts: 1669

Remove the volume control (1 grubscrew). Remove the balance control (2 screws). Remove the bass & tilt controls (1 grubscrew each). Remove the front panel (4 screws at the sides and one near the middle securing the PCB), leaving the button PCB behind. Squirt the cleaner behind each button, working each one 10 or 20 times. Reassemble, noting that the washer (if still present) goes on the middle PCB-securing screw, and making sure to leave a clearance behind the bass & tilt knobs so they don't scratch the panel.
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22-Oct-2019 01:11 AM

Fabian

Fabian

Posts: 102

I really just wanted to know if I need to peel the buttons from the switches before applying a cleaning fluid (and I was asking for confirmation that this requires removing the front facia. :) Anyway, I tried to followed the advice. On the 34 the button board is screwed to the front plate, so I unscrewed it to get access. Next, I DID pull the buttons from the switches (seemed obvious to me now). This left me with all the button switches accessible,but not really convenient for applying a cleaner.

The hooks and latches to the left and right looked like it should be easy to dismantle the switches completely.So here I went. This is adetail picture of the dismantled switch top. Note the tarnished surface of the contact plate. The switch base contacts did not look clean as well. Here you can see thefirst of them cleaned and some others in original status. I mechanically cleaned all theswitch tops andbases using a small slot screw driver, some grain 800 sandpaper and isopropyl alcohol.

Reassembled all the switches andput back on the buttons (probably after the one and only full cleaning during their lifetime). I managed to not lose any one of the miniature spring coils, contact plates or concave counter plates. It’s a fiddly business and I don’t necessarily recommend doing it.

Even more, since the result was visually perfect, but not technically.

Even though all the contacts look MUCH better now, I ended up with a problem. Once in a while, pressing the RADIO button (or pressing it a second time) changes the selected input to DISK. This mostly  happens with any of the filters and the steeper filter slope selected (which probably nobody is using nowadays), but also with no other button switch selected, from time to time.

What could be the reason here?

This is an issue 6 all-RCA board. No other updates have been applied so far, except from increasing the max. output voltage to 0.775V. I want to apply the EJP deluxe upgrade kittomorrow today.

 

>style>
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22-Oct-2019 11:59 AM

EJP

EJP

Posts: 1669

You don't need to remove the buttons from the switches. The contact part of the switch is behind the plastic part that the button mounts on. You just need to squirt between that and the PCB. No disassembly required. I did all this just a couple of weeks ago.
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22-Oct-2019 01:17 PM

Fabian

Fabian

Posts: 102

Once again, thank you, Esmond. So the idea is to have the cleaner creep into the contact area of the switch from the PCB side?

I already did it the complicated way and as I said, I can’t really recommend it. The danger of loosing one of those tiny springs is very real.

Looking at the board again, I noticed that the 4n7 capacitor (C44) is missing across the RADIO switch (S2). According to the schematics there should be a total of 6 capacitors on the button board assembly, but there are only 5 on my board. Is this normal?

https://abload.de/image.php?img=07switchescleanedasse5xjyz.jpg

Judging from the solder points on the back of the PCB, C44 has never been in place.

>style>
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22-Oct-2019 01:27 PM

Fabian

Fabian

Posts: 102

I need to correct myself.

C44 is actually on the main PCB. But there is an empty spot for it on the button board. Strange. Why would one NOT want to have it close to the switch? Isn't it meant for debouncing?

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22-Oct-2019 05:13 PM

Ton

Ton

Posts: 63

sorry, off-topic, but cool links Fabian :)

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22-Oct-2019 05:39 PM

Fabian

Fabian

Posts: 102

@Ton: Thank you. This bit of OT is OK with me. ;)


Back to my problem of the disk input being selected when pressing other buttons. I gave it another try today and it was actually worse than I described it before. Disc got selected on start up and after selecting another source I hardly needed to touch it to re-select. Sometimes it was impossible to select radio or cd. Also the clicking sound of the button was a tiny bit different ...

 

You probably guessed it by now: Yes. I DID in fact lose the spring of the disc switch without even noticing it! :(

 

Where are all these miracles when you need one? Well, right there. I looked under my desk and - believe it or not - immediately spotted the spring. Unbelievable! I had even vacuumed the place (liberally) this morning!

 

So I just had to dismantle the switch again (starting to get used to it), reassemble in correct order and all was well. Maybe I should play the lottery today.

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23-Oct-2019 02:43 AM

EJP

EJP

Posts: 1669

The contact area is on the PCB side, not on the button side, so removing the button buys you nothing.
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23-Oct-2019 12:26 PM

Fabian

Fabian

Posts: 102

You see me puzzled. At least on my (second) Q34 the switches look like this:

There is a non-movable white “base” held in place by the four pins soldered to the PCB.

https://abload.de/img/1switch3ykkg.jpg

These pins are really just the ends of two wire bridges running through holes in the base. There are hooks to the left and right of the base and a circular notch in the middle.

https://abload.de/img/2switchbasedetailjwjxy.jpg

The black “top” of the switch moves relative to the base, its center guide pin matches the notch. Lugs to both sides correspond to the hooks and keep the top from falling off. Inside the black plastic part there are three more parts. A small round conductive plate, a leaf spring and a coil spring.

https://abload.de/img/3switchtopcomponentsn5jp8.jpg

The coil spring sits on top. It pushes the button back out and keeps the disc from making contact after releasing it. Next comes the disc itself which shortens the left and the right wire bridge in the base, when the button is pushed. Finally, below the disc sits another spring, made from thin stamped metal. The convex tip should point to the black plastic top, the raised edges to the conductive disc.

https://abload.de/img/4switchtopassembledohjea.jpg

From what I see, the only area that would benefit from cleaning are the contact surfaces of the disc and the wire bridged, both located right between the white “base” and the black “top”. I can only speak for the buttons in my very own amp. Maybe there have been different versions?

>style>
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24-Oct-2019 10:09 PM

Joost Plugge

Joost Plugge

Posts: 971

I did also clean the switches, but it is not only a matter of cleaning, also there are mechanical problems, nowadays I simply replace the switches, they are still available. I think Stefaan should stock them, I will mail Stefaan with the correct info. The switches are used in the 34, 44, FM4 and the scepter of the 66. Cleaning them is messy and will not always give good results.

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25-Oct-2019 11:43 AM

Stefaan

Stefaan

Posts: 618


Replacement switches are available here:

http://www.dadaelectronics.eu/shop/components/switches/tactile-switch-d6-series-square-button-130-gf-100ma-at-32vdc


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